1. Field of the Invention
The present invention relates to a process for producing a urethane and a carbonic acid ester which comprises reacting a primary amine, an organic compound containing a hydroxyl group(s), carbon monoxide and molecular oxygen with one another by using a catalyst comprising mainly copper.
Urethanes are per se important compounds as substrate for carbamate based agricultural chemicals, and since they can easily be converted into isocyanates for producing polyurethanes, by heat treatment, there has recently been desired a process for producing them at low cost as intermediates for producing isocyanates without using phosgene which is poisonous.
On the other hand, carbonic acid esters are useful not only as starting materials for producing polycarbonates, but also as esterifying agents, solvents, etc.
2. Description of the Prior Art
Urethanes and carbonic acid esters have heretofore been produced by reacting phosgene with primary amines or alcohols, but in recent years, there have proposed various methods using no phosgene which is very poisonous.
The methods for producing urethanes without using phosgene are roughly divided into two groups, namely, methods of using nitro compounds as starting materials and methods of using primary amines as starting materials.
The methods using nitro compounds as starting materials comprise reacting a nitro compound such as nitrobenzene, an organic compound containing a hydroxyl group(s), such as an alcohol, and carbon monooxide with one another in the presence of a catalyst comprising mainly a compound of an element of the platinum group, e.g., palladium or rhodium, or selenium, and thereby producing a urethane reductively, and they are disclosed, for example, in British Patent Nos. 1080094 and 1402379. Japanese Patent Kokai (Laid-Open) Nos. 57-32250 and 57-32251 disclose methods for producing a urethane and a carbonic acid ester at the same time by reacting an aromatic nitro compound, an organic compound containing a hydroxyl group(s), and carbon monoxide with one another in the presence of a catalyst comprising mainly palladium.
On the other hand, the methods using primary amines as starting materials comprise using molecular oxygen or a nitro compound as an oxidizing agent, reacting a primary amine such as aniline, an organic compound containing a hydroxyl group(s), and carbon monoxide with one another in the presence of a catalyst comprising mainly a compound of an element of the platinum group, e.g., palladium, rhodium or ruthenium, and thereby producing a urethane oxidatively. These oxidative carbonylation methods are disclosed, for example, in Canadian Patent No. 1150292, U.S. Pat. Nos. 4490551, 4297501 and 4547322.
In the methods using a nitro compound or a primary amine as a starting material, a catalyst comprising a compound of an element of the platinum group or selenium is used, but since the main catalyst itself has only low urethane synthesizing activity, there have been developed catalytic systems consisting of combinations of the main catalyst and co-catalysts such as iron chloride, iron oxychloride, vanadium oxychloride, lithium hydroxide, halides and Lewis acids, or ligands such as pyridine and quinoline. Employment of these co-catalysts or ligands, however, is disadvantageous in that although the urethane synthesizing activity is improved, a complicated catalyst composed of many components is used, so that a troublesome procedure and a great cost are required for recovering, for reuse, the expensive compound of the element of the platinum group efficiently from the reaction mixture after the reaction.